1. Field
The present disclosure relates to a solid oxide electrolyte, a solid oxide fuel cell including the same, and a method of preparing the solid oxide electrolyte.
2. Description of the Related Art
Fuel cells are regarded as one of various alternative energy sources. Fuel cells can be categorized as a polymer electrolyte membrane fuel cell (“PEMFC”), a phosphoric acid fuel cell (“PAFC”), a molten carbonate fuel cell (“MCFC”), or a solid oxide fuel cell (“SOFC”), based on the type of electrolyte used.
An SOFC uses a solid oxide having ionic conductivity as an electrolyte. SOFCs have high efficiency and high durability, use various kinds of fuels, and can be manufactured at low cost.
An SOFC unit cell includes a membrane-electrode-assembly (“MEA”) which includes a solid oxide electrolyte and electrodes. Because SOFCs operate at a high temperature, such as 400 to 1200° C., the solid oxide electrolyte desirably has excellent sintering properties, high mechanical strength, and a wide range of driving temperature. For example, a solid oxide electrolyte having such properties may be yttria stabilized zirconia (“YSZ”).
In addition, an actual output voltage of an SOFC may be lower than a theoretical voltage due to polarization occurring inside the solid electrolyte or the electrodes. For example, the actual output voltage may be represented by the Equation below:V=Voci(Relectrolyte+Rcathode+Ranode)−ηcathode−ηanode  Equationwherein V denotes the actual output voltage, Voc denotes an open circuit voltage, ηcathode and ηanode denote electrodic polarization of the cathode and anode, respectively, I denotes a current, and Relectrolyte, Rcathode, and Ranode denote resistance of an electrolyte, resistance of a cathode, and resistance of an anode, respectively. Thus i(Relectrolyte+Rcathode+Ranode) denotes ohmic resistance polarization.
As shown in the equation above, as Relectrolyte increases, V is decreases. Thus, in order to increase V, the solid oxide electrolyte needs to have a low Relectrolyte, that is, a high ion conductivity. YSZ has low ion conductivity.
Accordingly, there remains a need for a solid oxide electrolyte having high ion conductivity in addition to excellent sintering properties, high mechanical strength, and a wide range of driving temperature.